BBC Homepage World Service Education
BBC Homepagelow graphics version | feedback | help
BBC News Online
 You are in: Sci/Tech
Front Page 
UK Politics 
Talking Point 
In Depth 

Leo Hollberg, NIST
For the last 50 years time and frequency have been kept using the caesium clock
 real 28k

Thursday, 12 July, 2001, 18:28 GMT 19:28 UK
World's most precise clock developed
By BBC News Online science editor Dr David Whitehouse

Researchers have developed a new type of atomic clock that is significantly more stable and therefore far more precise than the current technology in use.

Experiments suggest the clock is accurate to about one second in a 100 million years.

As clocks get better and better, the applications that people dream up just keep getting better and better

Scott Diddams, NIST
It works on the same basic principle that microwave atomic clocks have employed since the 1950s, but utilises optical (visible) light, which being of a higher frequency, provides more accurate timekeeping.

The new optical atomic clock's creators say that their new timepiece will provide "an even finer-grained view of the physical world."

"We've demonstrated for the first time the next generation of atomic clocks, which have the potential to be 100 to 1,000 times more accurate than the current caesium-based microwave clocks," said physicist Scott Diddams, whose team at the US National Institute of Standards and Technology (NIST) developed the new timepiece.

The clock will have a big impact in many fields, such as satellite navigation, the internet and electricity distribution - all depend on precise timing.

Astronomical precision

Clocks have come a long way in the past one thousand years. In 1088, the Chinese developed a water clock accurate to about 100 seconds a day.

In the 17th Century, pendulum clocks were accurate to about 10 seconds a day. By the 1930s, the most accurate clocks kept time to within a second over a three-day interval.

1760s: John Harrison's revolutionary H4 marine chronometer lost just under a second a day at sea
But it was with the introduction of atomic clocks, based on precisely measured microwaves emitted by specific atoms, that the precision of timekeeping became astronomical.

Atomic clock technology enabled scientists in 1967 to define the second as the period equal to 9,192,631,770 cycles of the radiation that corresponds to the transition between two energy levels of the ground state of the caesium-133 atom.

By 1995, the best atomic clocks were accurate to a second every 15 million years - and now they have become even better with the new NIST timepiece.

According to Dr Patrick Gill, head of wavelength standards at Britain's National Physical Laboratory (NPL), the new clock is an exciting development.

'Impressive technology'

He told BBC News Online: "It's an impressive display of technology that could eventually have many practical applications."

In current atomic clocks, transitions between energy levels in caesium atoms at microwave frequencies form the basis for measuring time.

It's an impressive display of technology

Dr Patrick Gill, NPL
Optical transitions occur at much higher frequencies than microwave transitions and thus provide a much finer timescale and more precise timekeeping.

Writing in the journal Science, Diddams and colleagues say their new clock is based on the optical frequency of a single cooled mercury ion (a mercury atom with one electron stripped off) linked to a laser oscillator - which acts rather like a traditional pendulum to produce the clock's "ticks".

Except, this clock is producing 1.064 quadrillion ticks per second - so many that a high-speed laser and an optical fibre link are then required to count them and so mark time.

Space navigation

The technology is likely to lead to more precise measurements of fundamental physical constants.

But more generally, precise timekeeping is important for things like high-speed data transmission, synchronizing television feeds, calculating bank transfers, and the sending of e-mail.

Power companies also use precise time to regulate power system grids.

Scott Diddams said advances in timekeeping technology tended to spur leaps forward in a lot of other fields. "As clocks get better and better, the applications that people dream up just keep getting better and better."

He said he envisaged future uses for the new clock in regulating precise orbits for satellites, deep-space navigation and linking together spacecraft. "You need very precise navigational tools for this," he added.

Search BBC News Online

Advanced search options
Launch console
See also:

21 Jul 98 | Sci/Tech
A clock the size of a pollen grain
07 Sep 98 | Sci/Tech
How bacteria tell the time
05 Feb 99 | Sci/Tech
Six pip salute
29 Dec 98 | Sci/Tech
Time to make history
Internet links:

The BBC is not responsible for the content of external internet sites

Links to more Sci/Tech stories are at the foot of the page.

E-mail this story to a friend

Links to more Sci/Tech stories